1. Field of the Invention
The present invention relates to a water-base polyurethane emulsion particularly useful as an adhesive or coating material for a polyolefin resin.
2. Description of the Prior Art
Water-base polyurethane emulsions are used in various fields, for instance, as adhesive, impregnation agents or coating agents. A variety of excellent polymers ranging from soft elastomers to hard plastics are obtainable by reacting various types of polyisocyanate compounds with active hydrogen compounds having at least two active hydrogen atoms such as hydroxyl groups or amino groups. They are of great interest particularly in the field of adhesives, since they exhibit an excellent adhesive property to a variety of substrates such as plastics, metals, woods and papers.
However, the conventional water-base polyurethane emulsions are hardly bonded to a polyolefin resin material having little functional groups in its structure, such as a polyethylene resin or a polypropylene resin. Accordingly, their application in this respect has been limited. As a method for improving the adhesion to a polyolefin resin material, it is common to conduct corona discharge treatment to activate the resin surface. However, even to such a surface-treated polyolefin resin material, none of the conventional water-base emulsions including water-base polyurethane emulsions show adequate adhesion to a practical extent.
Polyolefin resins have excellent electric, mechanical and chemical properties, and there is an increasing demand for such polyolefin resins in various fields. Under the circumstances, it is an important objective in the market to develop a water-base emulsion adhesive which satisfies the requirements for non-pollution, fire-safety, conservation of resources, etc.